A broad range of products is packed in airtight conditions in order to prolong shelf life, to guarantee its quality, or to preserve its sterility. Such products range from food and beverages to medical, electrical and pharmaceutical items being liquids, solids, gasses, or a combination thereof. A crucial point in the packaging process is to ensure a high quality sealing of the package. Seal quality encompasses several issues such as airtightness, inclusions, strength and visual appearance. If the seal does not meet the quality requirements, the product can be rejected by the consumer based on the visual appearance of the package, or in case of no airtightness, the quality of the product inside the package could rapidly deteriorate in terms of visual appearance, flavor, mouth feel, sterility and microbial safety and, hence, consumer health. Inappropriate seal quality is a frequently occurring problem in the packaging industry. Given that a defective seal often leads to the rejection by the consumer of the packaged product, the packaging industry is particularly sensitive to this problem. In many cases the monitoring of the individual packages is still performed manually, which is a tiresome and unpleasant occupation. It is an aim of the present invention to provide an inspection device for the on-line monitoring of the seal quality of different types of packages and more particularly of packages processed using a heat seal process.
During the process of heat sealing, the (two or more) thermoplastic films of a package are brought in contact with each other, and the temperature is increased so that fusion of the films is achieved. The films are brought into contact and pressure is exerted on them by positioning the films between two or more sealing bodies that are pressed against each other. Different mechanisms to move the sealing bodies are used in practice, such as rotating shafts, or pneumatic/hydraulic cylinders. Also the methodology used to increase the temperature can vary from one type of equipment to another. It can be achieved by rotating wheels, by resistance elements, dielectric or by ultrasonic vibrations, amongst others. Since the sealing process always involves a movement of at least one of the sealing bodies, wearing of the machinery is inevitable. This degree of wearing (for instance in the bearings or on the sealing bodies) affects the characteristics of the sealing process and the state of the machinery needs to be monitored adequately. The quality of the sealing is also influenced by the temperature of the process, the pressure exerted on the thermoplastic films, the cleanness of the sealing bodies, the positioning of the films relative to the sealing bodies, the quality of the film and the material to be packaged. Besides these factors, the presence of foreign bodies in between the thermoplastic films, or between the films and the sealing bodies, clearly affects the seal quality. This high number of dynamic variables affecting the operation and efficacy of the sealing equipment precluded the prediction of the seal quality based on the monitoring of the behavior of the sealing device at the moment of sealing. Indeed, the different seal inspection systems that are commercially available evaluate the seal quality based on the monitoring of the characteristics of the package. Three types of such inspection devices can be discriminated: (1) A sealing inspection system based on applying a nondestructive pressure on the package and to repeat this measure at two different times. When the package is not airtight, a difference in reading between these two moments will be noticed due to the fact that air has moved out of the package [Packaging Technologies & Inspection, http://www.ptipacktech.com/inspection/foodpackages/pressuretesting.cfm]. (2) A camera vision inspection system in which an image of the package or seal is taken and analysed [Perceptics, http://www.perceptics.com/sealsafe_pouch.html]. (3) An ultrasonic inspection system that generates a fingerprint of the seal [Packaging Technologies & Inspection, http://www.ptipacktech.com/inspection/foodpackages/sealintegritytesting.cfm].
Next to the above-mentioned systems, JP2001240024 describes a system for the detection of the squeezing of an article to be packaged between the sealing elements of a bag-making filling machine. The squeezing of the product to be packaged is detected by analysing the acoustic signal emitted by the product to be sealed at the moment of sealing. More specifically, the sound pressure level within a specified frequency of the acoustic signal is compared to a fixed reference value. When the measured sound pressure value exceeds the fixed reference value the device considers that a squeezing of the product occurred during the sealing process. Essentially, the device of JP2001240024 discriminates between the acoustic signal associated with the normal operation of the sealing device and the acoustic signal associated with the squeezing of a product between the sealing elements.
The present invention provides a system for the on-line inspection of the quality of the sealing of packages based on the observation of the behavior of the sealing bodies during the sealing process. The system has the advantages that it can easily be applied on different types of heat seal equipment and that it takes into account the variation of the behavior of the sealing bodies related to the wear of the equipment, the variation of the package quality, the variation in the positioning of the package in the sealing device, etc. . . . Moreover, the flexibility and sensitivity of the system of the present invention allows the systematic and consistent detection of minor anomalies in the sealing process. The anomalies detected in the sealing process can be extrapolated towards a prediction of the quality of the seal. This information is then used to decide whether or not the seal quality of a given package allows further processing and distribution of said package.